The present invention relates to a method and apparatus for determining the fluid flow velocity in a pipeline. In particular, the invention utilizes the technique of measuring the dynamic pressure fluctuations produced by turbulent flow to determine the flow rate. The above referenced patents disclose the use of a single pressure transducer to detect the dynamic pressure fluctuations caused by turbulent flow to determine the flow rate in the pipeline. The pending application discloses to use of two identical transducers which are mounted diametrically opposite to each other in the pipeline. Acoutic pressure fluctuations transmitted through the fluid are sensed identically by both transducers. The turbulent pressure fluctuations sensed by the two transducers are, however, independent of each other. Therefore, from the difference in the dynamic pressures measured by the two transducers, one can determine the flow rate in a single phase flow system.
All of the above methods have provided satisfactory results for measuring flow rates in pipelines where great accuracy is not required. The systems disclosed in the two patents have been used extensively to monitor the production from oil wells to determine when the production had fallen to a level that required remedial action or a workover of the well. While the systems are satisfactory, they did require that the flow measuring instruments be calibrated in place on the pipeline. The single transducer method works well for two phase flow but has the following disadvantage when used for single phase flow measurement. The instrument calibration depends strongly on flowline geometry, both near and far, and on acoustic pressure sources in the flowline. In practical oil field operations, variations in the flowline geometry and in acoustic pressure sources occur as valve positions are changed and pumps are turned on or off. Therefore, the measured flow rate signal displays considerable scatter even if the flow rate remains constant.
While these problems occur in two-phase flow systems as well, they are more acute for single-phase flow measurement. In these instances it was normally impossible to use the systems disclosed in the prior patents unless one was willing to accept rather large errors in the measured flow rate.